Neurodegeneration has been proposed as one of the possible pathophysiological mechanisms underlying diabetic retinopathy (DR). In this prospective cohort study, we investigated parafoveal cone density in different stages of DR using adaptive optics (AO) retinal imaging.

Methods

An AO retinal camera (rtx1; Imagine Eyes, Orsay, France) was used to acquire images of parafoveal cones from patients with diagnosis of diabetes mellitus with or without retinopathy and from healthy controls with no known systemic or ocular disease. Eyes with myopia (> 10 diopters), media opacity, current macular edema, or any coexistent retinal diseases other than DR were excluded. The final image produced by the AO camera is equivalent to ≈ 1.2 × 1.2 mm (4° × 4°) based on axial length (AL) of the eye. The density of the parafoveal cones was calculated in 100 × 100 µm square located at 300 and 500 µm from the foveal center (a minimum of 250 µm from the foveal center is recommended for feasible cone assessment) along nasal, temporal, superior and inferior quadrants. The measurements (cones/mm2) were done using automated AOdetect Ver. 0.1. Software provided by the manufacturer. AL were measured using non-contact biometry (IOL Master®; Carl Zeiss Meditech, Germany). Correlation between diabetes control (Hb1Ac) and severity of DR with cone density was analyzed using Spearman correlation test.

Results

Ten subjects (10 eyes) with no known ocular or systemic diseases and 14 (17 eyes) with diabetes were included (Table). Among those with diabetes, 4 patients (5 eyes) did not have retinopathy, 3 (4 eyes) had mild NPDR, 5 (6 eyes) had moderate NPDR and 2 (2 eyes) had severe NPDR. The mean Hb1Ac among patients with diabetes was 8.5 ±2. A significant difference (P< 0.001) in cone density was found between healthy controls and moderate/severe NPDR group (figure); however, no statistical significance was found between controls and no retinopathy or mild NPDR groups.<br /> An inverse relationship between cone density and Hb1Ac was observed in all parafoveal regions; however, no relationship could be correlated for the duration of diabetes.

Conclusions

Patients with diabetes may have loss of photoreceptors with increasing severity of DR. AO provides assessment of photoreceptors, which may allow better understanding of the disease pathology.